1. Field of the Invention
The present invention relates to a hydraulic circuit of a tilt device for a marine propulsion unit.
2. Description of the Related Art
As a tilt device for a marine propulsion unit, there is a structure in which the marine propulsion unit is supported to a mounting bracket fixed to a hull in a freely tilting manner, a tilt cylinder device supported to a side of the mounting bracket is connected to the marine propulsion unit, and a trim cylinder device supported to a side of the mounting bracket is brought into contact with the marine propulsion unit. In this tilt device, the tilt cylinder device sections a first chamber which receives a piston rod and a second chamber which does not receive the piston rod, by a piston. The piston of the tilt cylinder device is provided with an absorber valve allowing an oil to flow from the first chamber to the second chamber. A trim cylinder device sections a first chamber which receives a piston rod and a second chamber which does not receive the piston rod, by a piston. The tilt device has a working fluid supply/discharge device which extends and contracts the tilt cylinder device and the trim cylinder device so as to tilt the marine propulsion unit by supplying and discharging the working fluid within a tank pressure fed by a pump to the tilt cylinder device and the trim cylinder device.
The working fluid supply/discharge device is provided with a first fluid passage communicating the pump with the first chamber in the tilt cylinder device via a first switching valve and a second fluid passage communicating the pump with the second chamber in the tilt cylinder device via a second switching valve. The working fluid supply/discharge device communicates the first chamber in the trim cylinder device with the tank and communicates the second chamber in the trim cylinder device with the second fluid passage. Further, at a time of tilt-down operation of the pump, the working fluid supply/discharge device opens the first switching valve due to a discharge pressure of the pump and opens the second switching valve due to a line pressure of the first fluid passage so as to make it possible to operate the tilt cylinder device and the trim cylinder device downwardly. Further, at a time of tilt-up operation of the pump, the working fluid supply/discharge device opens the second switching valve due to the discharge pressure of the pump and opens the first switching valve due to the line pressure of the second fluid passage so as to make it possible to operate the tilt cylinder device and the trim cylinder device upwardly.
Accordingly, at a time of tilt-down operation of the marine propulsion unit, the oil discharged from the pump enters into the first chamber of the tilt cylinder device through the first switching valve, and the oil in the second chamber of the tilt cylinder device returns to the pump through the second switching valve so as to contract the tilt cylinder device. When the marine propulsion unit enters into a trim range from a tilt-up range due to the contraction of the tilt cylinder device, the trim cylinder device is brought into contact with the marine propulsion unit so as to be contracted due to a contracting force of the tilt cylinder device, the oil in the second chamber of the trim cylinder device returns to the pump through the second switching valve, and the oil supplied from the tank enters into the first chamber of the trim cylinder device.
Further, at a time of tilt-up operation of the marine propulsion unit, the oil discharged from the pump enters into the second chamber of the tilt cylinder device and the second chamber of the trim cylinder device through the second switching valve, the oil in the first chamber of the tilt cylinder device returns to the pump through the first switching valve, and the oil in the first chamber of the trim cylinder device returns to the tank so as to extend the tilt cylinder device and the trim cylinder device. After the marine propulsion unit reaches the maximum trim-up position within the trim range, the trim cylinder device stays at the maximum up position and only the tilt cylinder device continues the extending operation.
At a time of tilt-lock operation at which the marine propulsion unit is neither tilted down nor tilted up, the operation of the pump is stopped. Accordingly, none of the oil in the first chamber of the tilt cylinder device and the oil in the second chamber can move, whereby the tilt cylinder device can not be extended or contracted, so that the marine propulsion unit is tilt-locked.
Further, if driftwood or the like collides with the marine propulsion unit during forward movement of the hull and an impact force in an extending direction is applied to the tilt cylinder device, the oil in the first chamber of the tilt cylinder device (which becomes highly pressurized) opens the absorber valve in the piston so as to relieve the oil in the first chamber to the second chamber. Accordingly, the tilt cylinder device is immediately extended and the marine propulsion unit jumps into a tilt-up position, whereby the impact force is absorbed.
Accordingly, in the tilt device mentioned above, the tilt cylinder device is not provided with a free piston for returning the piston position after absorbing the impact force generated due to the collision of the driftwood or the like to the piston position before absorbing the impact force, in the second chamber. Accordingly, the tilt cylinder device extending due to the absorption of the impact force is tilted down until the marine propulsion unit is brought into contact with the trim cylinder device or until the trim cylinder is completely expended, due to an empty weight of the marine propulsion unit.
Then, in the process mentioned above in which the tilt cylinder device tilts down due to the empty weight of the marine propulsion unit, the second chamber of the tilt cylinder device is pressurized by the empty weight of the marine propulsion unit, the oil flows into the second chamber of the trim cylinder device connected to the second chamber of the tilt cylinder device by the second oil passage, and the piston rod of the trim cylinder device protrudes until the piston rod is brought into contact with the marine propulsion unit or completely extends. At this time, the oil in the first chamber of the trim cylinder device rapidly returns to the tank, so that an internal pressure of the tank is rapidly increased, whereby there is a risk of a failure such as a breakage to a seal portion of the tank or the like.
Embodiments of the present invention provide a system to prevent internal pressure of a tank from increasing after absorbing an impact force generated due to a collision with driftwood or the like, in a tilt device for a marine propulsion unit provided with a tilt cylinder device and a trim cylinder device.
In some embodiments, there is provided a hydraulic circuit of a tilt device for a marine propulsion unit in which the marine propulsion unit is supported to a mounting bracket fixed to a hull in a freely tilting manner, a tilt cylinder device is supported to a side of the mounting bracket is connected to the marine propulsion unit, a trim cylinder device supported to a side of the mounting bracket is brought into contact with the marine propulsion unit, the tilt cylinder device is structured such as to section a first chamber which receives a piston rod and a second chamber which does not receive the piston rod, by a piston, and be provided with an absorber valve allowing an oil to flow from the first chamber to the second chamber in the piston and with no free piston in a lower portion of the piston, the trim cylinder device sections a first chamber which receives a piston rod and a second chamber which does not receive the piston rod, by a piston, and the tilt device has a working fluid supply/discharge device which extends and contracts the tilt cylinder device and the trim cylinder device so as to tilt the marine propulsion unit by supplying and discharging the working fluid within a tank pressure fed by a pump to the tilt cylinder device and the trim cylinder device, wherein a throttle is provided in a communicating passage connecting the first chamber of the trim cylinder device to the tank.
In some embodiments, there is provided a hydraulic circuit of a tilt device for a marine propulsion unit in which the marine propulsion unit is supported to a mounting bracket fixed to a hull in a freely tilting manner, a tilt cylinder device is supported to a side of the mounting bracket is connected to the marine propulsion unit, a trim cylinder device supported to a side of the mounting bracket is brought into contact with the marine propulsion unit, the tilt cylinder device is structured such as to section a first chamber which receives a piston rod and a second chamber which does not receive the piston rod, by a piston, and be provided with an absorber valve allowing an oil to flow from the first chamber to the second chamber in the piston and with no free piston in a lower portion of the piston, a trim cylinder device sections a first chamber which receives a piston rod and a second chamber which does not receive the piston rod, by a piston, and the tilt device has a working fluid supply/discharge device which extends and contracts the tilt cylinder device and the trim cylinder device so as to tilt the marine propulsion unit by supplying and discharging the working fluid within a tank pressure fed by a pump to the tilt cylinder device and the trim cylinder device, wherein the first chamber of the trim cylinder device is communicated with the tank, and also with the first chamber of the tilt cylinder device.